Aetna CEO: Obamacare In A 'Death Spiral' Heading Into 2018. Aetna and Humana have called off their deal amid government concerns over competition. Here's a look back at six pivotal moments that led to this. Aetna and Humana have called off their deal amid government concerns over competition.
For the plant genus, see Synapsis (plant). Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Synapsis takes place during prophase I of meiosis.
Chemical neurotransmission occurs at chemical synapses. In chemical neurotransmission, the presynaptic neuron and the postsynaptic neuron are separated by a small gap â the synaptic cleft. The synaptic cleft is filled with extracellular fluid (the fluid bathing all the cells in the brain).